According to kelly blue book, assuming your car is equipped with standard equipment for its trim and has ~150,000 miles, you can expect about $1,200 to $1,500 by selling it private party. Selling on Craigslist is very straightforward: take good picures, write a good description, show the car, receive payment, sign over title (obviously very simplified). I wold encourage you to take this as an opportunity to transition to one car, you camry isn't getting any younger.
The question you and your wife need to ask yourselves is: What do we want out of a car? Right now, your RAV4 fits your needs. You own it, it will accommodate both your kids (the door seats aren't the worst things in the world), and can still haul other things in the trunk. Do you need more space? Are other people in your car wit both the kids? Will you be taking road trips? If no to any of these, your current car will be more than adequate. If you can find a really good reason for the van, then get a used one with the expectation that you won't be buying another car for a long time.